Newbie please bare with me, just got my 1985 truck and I've figured out how and when the cargo light works. My problem is still interior lights, I have none and working on it.
Dome light. Found 7.5 amp fuse to be good. Cleaned dome light switch connections and now manually the dome light works but not when opening doors. Behind the driver left door kick panel I found the door jam switch un-plugged. Looks like something was cut out because there is nothing for it to plug into but I don't know what. I did find a solid red wire that has been cut with a bare end near the interior fuse box. When the door jam switch is connected to this red wire the buzzer engages(nice and loudly). Dome light still doesn't work however and I'm really not interested in the buzzer coming on just by opening the door.

Gotta tell us what year/model you are working on.

1985 truck xtra=cab 4x4 base model.